1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming method, a computer program, and a computer-readable storage medium.
2. Description of the Related Art
A known image forming apparatus forms an electrostatic latent image on a photosensitive element through optical writing, temporarily transfers a toner image of each color obtained through development of the electrostatic latent image onto an intermediate transfer member, such as an intermediate transfer belt, to thereby superimpose the toner images of different colors one on top of another on the intermediate transfer member, and transfers and fixes the toner image of each color from the intermediate transfer member onto and in paper, thereby obtaining a color image.
During continuous printing operations performed by such an image forming apparatus, a known color shift correcting unit simultaneously forms a print image in an image forming area of the intermediate transfer belt and a pattern for detecting a color shift amount in an area outside the image forming area and detects with, for example, a sensor the color shift amount from the pattern on the area outside the image forming area, thereby correcting the color shift according to the detected color shift amount.
Additionally, some copiers and multifunction peripherals (MFPs) that incorporate a plurality of functions of, for example, a copier, facsimile, and printer in one housing form a toner test pattern on the intermediate transfer belt and cause sensors to detect the toner test pattern in order to make image adjustments including color shift correction and density correction. The sensors that detect the test pattern are disposed at positions different from each other in a main-scanning direction. The test pattern is formed at a position on the intermediate transfer belt so as to be detected by each of the sensors.
To reduce downtime during which no print operations can be performed due to image adjustments, a test pattern is formed on either end outside a main scanning image area concurrently with printing for image adjustments.
In order to perform color shift correction during continuous printing operations, Japanese Patent No. 3743516 discloses a method for correcting a color shift amount, in which a color shift detecting pattern is formed simultaneously with a print image during continuous printing operations.
The related-art color shift correcting unit during continuous printing operations, however, performs the correction during the continuous printing operations. Thus, depending on timing at which the correction is reflected, it may take a long time before a correction amount is reflected, which results in a faulty image occurring before the correction amount is properly reflected. Alternatively, an approach has been taken to perform color shift correction at longer printing intervals allowed with the aim of preventing the faulty image from occurring due to the long time required before the color shift correction amount is reflected. This has led to time loss.
The technique disclosed in Japanese Patent No. 3743516 corrects the color shift amount during continuous printing operations by temporarily interrupting a print operation at some time and allowing longer printing intervals at other times. Thus, the technique disclosed in Japanese Patent No. 3743516 involves loss of time, such as time during which the print operation is temporarily interrupted and time allowed for longer printing intervals, specifically, what is called time-related loss.
The present invention has been made in view of the foregoing situation and it is an object of the present invention to perform color shift correction in an image forming apparatus without allowing time loss or time-related loss to occur.